The present invention relates to a method of display suitable for use on a mobile body such as an automobile or the like to detect the present or current position of the same and to display a map showing the area in the vicinity of the point of detection, a method of storing image information used for purposes including providing such a display or the like, a display apparatus and a navigation apparatus employing such a method of display and such a method of storing image information, and an automobile carrying such a navigation apparatus.
Various navigation apparatuses loaded on a mobile body such as an automobile or the like have been developed. For example, such a navigation apparatus is comprised of a means for reading a mass data recording medium such as a CD-ROM storing data of road maps, a means for detecting a present or current position and a display apparatus for displaying a road map for an area in the vicinity of the detected current position based on data read from the data storage medium. In this case, the means for detecting the current position may employ a positioning system referred to as a GPS (global positioning system) utilizing a signal transmitted from a satellite for positioning (hereinafter simply referred to as a GPS), an autonomous navigation (self-contained navigation) method wherein the current position of a vehicle is measured by tracing the transition of the current position from the starting point based on information including the traveling direction and traveling speed of the vehicle, or the like.
The data of a road map for an area in the vicinity of the current position detected by such a current position detecting means is read from a mass data recording medium such as a CD-ROM or the like. Then, a display signal (video signal) for displaying the road map is generated and this video signal is supplied to a display apparatus (which utilizes a liquid crystal display panel in most cases) to display the road map in the vicinity of the current position.
It takes time for such display apparatuses including such a navigation apparatus or the like to display an image such as a map or the like on the display thereof after the apparatuses are activated. For example, when the navigation apparatus is activated, a controller in the navigation apparatus performs processes for determining the current position and reading a map information on an area in the vicinity of the determined position from a recording medium such as a CD-ROM or the like. Such processes are somewhat time-consuming, and some additional time is also required to draw a map based on the read map information and to obtain a display signal therefrom. Therefore, it has taken several tens of seconds for the apparatus to actually display a map of roads in the vicinity of the current position on the display apparatus thereof after the power supply of the apparatus is turned on.
The problem of the long time spent before a map is displayed not only in activating the apparatus by turning the power supply on but also in displaying a map or the like based on information read from a newly loaded recording medium in the case of the replacement of a recording medium such as a CD-ROM or the like loaded in the apparatus. Specifically, since the amount of map data recordable on, for example, a single CD-ROM loaded in the navigation apparatus is limited, it is often required to replace such a CD-ROM when a need for map information on areas recorded on other CD-ROMs arises as the travel proceeds or when there is a need for information for displaying a more detailed map even for the same area. In such cases, it has taken several tens of seconds before an image of a map or the like is newly displayed because the apparatus performs a process of reading a map information or the like from a newly loaded disk and a displaying process based on the read information similarly as encountered in the above-described case of activating the apparatus by turning the power supply on.
When it takes a long time to display a map or the like as encountered at the time of the activation of an apparatus or the replacement of a recording medium as described above, a user can not confirm his or her position on the map in such a period, which reduces the convenience of use of a navigation apparatus. Although a navigation apparatus has been described as an example, the same problem arises in various display apparatuses which display images and the like based on information read from similar recording media.